linux-kernel - Re: [linux-usb-devel] 2.6.20 kernel hang with USB drive and vfat doing ftruncate

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Date:	Wed, 21 Feb 2007 16:50:23 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	<linux-usb-devel@...ts.sourceforge.net>,
	Pete Zaitcev <zaitcev@...hat.com>, Greg KH <gregkh@...e.de>,
	Kumar Gala <galak@...nel.crashing.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [linux-usb-devel] 2.6.20 kernel hang with USB drive and vfat
 doing ftruncate

On Wed, 21 Feb 2007, Andrew Morton wrote:

> On Wed, 21 Feb 2007 16:22:17 -0500 (EST)
> Alan Stern <stern@...land.harvard.edu> wrote:
> 
> > On Wed, 21 Feb 2007, Andrew Morton wrote:
> > 
> > > > > It seems like usb-storage and aio are completely off in the weeds.   
> > > > > Ideas?
> > > > 
> > > > It seems usb-storage should remove some kmalloc and use mempool() for
> > > > urb...  Is someone working on this? And idea?
> > > 
> > > I think Pete said that we're supposed to be using GFP_NOIO in there.
> > 
> > We _are_ using it.
> 
> How admirably prompt.

Shucks, we've been using it for years...

> > > Not that it'll help much: the VM calls throttle_vm_writeout() for GFP_NOIO
> > > and GFP_NOFS allocations, which is a bug.  Because if the caller holds
> > > locks which prevent filesystem or IO progress, we deadlock.
> > > 
> > > I'll fix the VM if someone else fixes USB ;)
> > 
> > What else needs to be fixed?
> 
> Would be nice if someone can confirm that this fixes it:

Not having experienced the problem, I can't confirm the fix.  However...

> +	if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) {

Is that really the correct test?  I don't know enough about the memory 
management subsystem to say one way or the other.  What's special about 
having both flags set?

> +		/*
> +		 * The caller might hold locks which can prevert IO completion
--------------------------------------------------------------^  Typo

Although perhaps "prevert" is an acceptable neologism in this context.

> +		 * or progress in the filesystem.  So we cannot just sit here
> +		 * waiting for IO to complete.
> +		 */

Alan Stern

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